Electromagnetic actuators have a wide variety of uses. In addition to the application in medium-voltage switches as controlled actuation of the movable contacts, such actuators can also be used in machines and in switches.
Single-coil and two-coil electromagnets constitute prior art in terms of the electromagnetic drive for medium-voltage vacuum circuit breakers. As has already been mentioned above, the electromagnetic has the function of moving the movable contact of the vacuum chamber towards the fixed contact in the event of a connection and of tensioning a contact pressure spring with an excess stroke.
In order to start the movement, a current is passed through the coil of the electromagnet. The connected position is then held, counter to the force of the contact pressure spring, with the aid of one or more permanent magnets. Current in the coil used as the connection coil is then no longer required.
In order to disconnect the switch, in the case of a two-coil actuator, a current is passed through a disconnection coil which initially weakens the holding force of the permanent magnets to such an extent that the contact pressure spring can no longer be held and the movable contact opens. As the disconnection movement continues, an opening force can be produced by the disconnection coil.
In the case of a single-coil electromagnet, the disconnection can essentially only be initiated by the coil. The continuation of the disconnection is then determined by the contact pressure spring and by a separate disconnection spring.
Existing single-coil actuators are often of rotationally symmetrical design. This can prevent them from being matched in a simple manner to another rated short-circuit current since another diameter needs to be selected for a change in the air gap area. All parts can therefore in each case only be used for one size.